In general, a refrigerant compressor may be applicable to a vapor compression type freezing cycle (hereinafter, abbreviated as a “freezing cycle”), such as a refrigerator, an air conditioner or the like. For a refrigerant compressor, there has been introduced a constant speed compressor driven at a predetermined speed or an inverter type compressor in which its rotation speed is controlled.
A refrigerant compressor can be typically classified into a hermetic type compressor in which a drive motor which is an electric motor and a compression unit operated by the drive motor are provided together in an inner space of the sealed casing, and an open type compressor in which the drive motor is separately provided at an outside of the casing. The hermetic compressors are mostly used for household or commercial freezing equipment.
Furthermore, a refrigerant compressor can be classified into a reciprocating type, a scroll type, a rotary type, and the like according to its refrigerant compression method. The rotary compressor uses a method of compressing refrigerant using a rolling piston performing an eccentric rotational movement in a compression space of the cylinder and a vane brought into contact with the rolling piston to partition the compression space of the cylinder into a suction chamber and a discharge chamber.
In recent years, there has been known a compound rotary compressor having a plurality of cylinders in which a rolling piston and a vane are independently provided for the plurality of cylinders to compress refrigerant using one drive motor. The compound rotary compressor can be also classified into a variable capacity type rotary compressor in which a plurality of cylinders are independent from one another to independently compress refrigerant and a two-stage rotary compressor in which a plurality of cylinders are communicated with one another to sequentially compress refrigerant.
On the other hand, scroll compressor is a compressor in which a fixed scroll is fixed to an inner space of container, and an orbiting scroll is engaged with the fixed scroll to perform an orbiting movement, and two pairs of compression chambers consisting of a suction chamber, an intermediate pressure chamber and a discharge chamber are continuously formed between a fixed wrap of the fixed scroll and an orbiting wrap of the orbiting scroll.
The scroll compressor may perform inhalation, compression and discharge cycles in a smoothly sequential manner while obtaining a relatively high compression ratio compared to other types of compressors to obtain a stable torque, and thus widely used for refrigerant compression in air conditioning units, and the like. However, the scroll compressor should be formed such that the fixed wrap is engaged with the orbiting wrap, and thus is difficult in fabrication compared to other compressors, and as a result, the compound or two-stage scroll compressors have not been widely developed.